When high-speed transmission is carried out in mobile communications, the effect of delayed waves due to multipath propagation cannot be ignored, and transmission characteristics degrade due to frequency selective fading. Therefore, multicarrier methods such as OFDM (Orthogonal Frequency Division Multiplexing) are now attracting attention as one kind of technology for combating frequency selective fading. A multicarrier method is a technology that achieves high-speed transmission by transmitting data using a plurality of carriers (subcarriers) whose transmission speed is suppressed to a level at which frequency selective fading does not occur. With the OFDM modulation method, in particular, the subcarriers on which data is placed are mutually orthogonal, making this the multicarrier modulation method offering the highest spectral efficiency. Moreover, the OFDM modulation method can be implemented with a comparatively simple hardware configuration. For these reasons, OFDM is an object of particular attention, and various related studies are being undertaken.
As one example of such studies, a technology has been developed whereby duplication (so-called “repetition”) of transmit data is performed, and transmission is performed by OFDM (Non-patent Document 1).
A technology has also been developed whereby, in a multicarrier method, maximal-ratio combining type transmission power control is performed according to overall subcarrier quality information—that is, the lower the channel quality level of a subcarrier, the lower its transmission power is made, and the higher the channel quality level of a subcarrier, the higher its transmission power is made (Patent Document 1, Patent Document 2).
Hereinafter, for convenience, transmission by means of an OFDM method (or multicarrier method) will be referred to as “OFDM (or multicarrier) transmission,” and transmission in which maximal-ratio combining type transmission power control is performed will be referred to as “maximal-ratio combining transmission.”
Non-patent Document 1: Maeda, Atarashi, Kishiyama, Sawahashi, “Performance Comparisons between OFCDM and OFDM in a Forward Link Broadband Channel”, Technical report of IEICE, RCS2002-162, August 2002
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-358008
Patent Document 2: Japanese Patent Application Laid-Open No. HEI 11-317723